Clean the metal of all oxidation, scale, oil, dirt,
or other foreign matter. Regardless of the type of
joint used, proper cleaning of the metal is essen-
tial. For best results, use a stainless steel wire
Check all electrical circuit connections to make
sure they are properly connected and all fittings
Be sure the torch is the right type and capacity
for the current at which most of the welding will
be done. Some manufacturers offer different
torches for different ranges of welding current.
Check the size, appearance, and position of the
tungsten electrode in the torch. Ensure that the
electrode diameter and nozzle size meet the
manufacturers recommendations. The tip
should be properly shaped as discussed earlier
(refer to figure 8-9). The electrode should extend
beyond the end of the gas cup a distance ranging
from 1/8 to 3/16 of an inch for butt welding and
1/4 to 3/8 of an inch for fillet welding. Check the
electrode for positioning and good electrical con-
tact. The electrode should be clean and silvery. A
dirty tungsten electrode can usually be cleaned
satisfactorily with a fine emery cloth. If severely
contaminated, the electrode should be replaced
or the tip broken off and dressed on a grinding
wheel. A contaminated tungsten electrode and a
good tungsten electrode are shown in figure 8-12.
Check the ground cable connections to the work-
piece. The connections should be periodically
checked after welding begins because they tend
to work loose. When this happens, the welding
Set the machine for the correct welding amper-
age. (Follow manufacturers recommendations.)
Open the cylinder valve and adjust the gas flow.
Before welding, check the connections on the gas
supply for leaks with soapy water.
If using a water-cooled torch, turn on the water.
Be sure the water pressure is not higher than
recommended by the torch manufacturer.
GTA WELDING PROCEDURES
As we discussed in chapter 3, the detailed methods
and practices used to prepare a particular weldment are
called the welding procedure. We also said that the
Figure 8-12.Contaminated and good tungsten electrode.
Figure 8-13.Torch position for the starting swing to strike
procedure for a particular welded joint includes many
variables. The same variables that must be considered
for other welding processes also must be considered for
gas shielded-arc welding. Some of the variables that you
must consider include the following: type of base metal,
the joint design, the welding position, the type of shield-
ing gas, and the welding machine setting.
Starting the Arc
Before starting the arc, you should form a ball on
the end of the electrode for ac welding. To do this,
simply set the current to DCRP and strike an arc for a
moment on a piece of carbon or a piece of copper. The
ball diameter should be only slightly larger than the
original diameter of the tungsten electrode.
When starting the arc with an ac high-frequency
current, you do not have to bring the electrode into
contact with the workpiece. To strike the arc, you must
hold the torch in a horizontal position about 2 inches
above the work surface, as shown in figure 8-13. Then